Performance Characterization of Supported Iron Nanocatalysts for Fischer-Tropsch Synthesis

This study aimed to develop oxide-supported iron-based nanocatalyst and establish the particle-size dependence of the supported iron nanocatalyst in the Fischer-Tropsch synthesis (FTS) reaction. Iron nanocatalyst was synthesized using impregnation method at 3, 6, 10, and 15 wt % on SiO2 and Al2O3-SiO2 supports. Effects of iron loadings and catalyst supports on the physicochemical properties of supported iron nanoparticles were investigated using N2 physical adsorption, temperature-programmed reduction and electron microscopy. The performance of the supported iron nanocatalysts in the Fischer-Tropsch synthesis (FTS) was studied in a fixed-bed microreactor at atmospheric pressure. The average sizes of iron nanoparticles were 5.8 ± 1.2, 8.6 ± 1.1, 12.6 ± 1.3 and 13 ± 1.2 nm for the 3, 6, 10 and 15 wt% Fe on SiO2, respectively. At lower iron loading (3 and 6 wt %) on SiO2, iron nanoparticles were more uniformly distributed compared to those at higher loadings. Using the Al2O3-SiO2 support, the average sizes of iron nanoparticles for the 3, 6, 10, and 15 wt% Fe were 6.2 ± 1.8, 10 ± 2, 14.5 ± 3.3, and 17.8 ± 5.3 nm, respectively.
The 3 and 6 wt% Fe/SiO2 resulted in 60 % and 54 % CO conversion, respectively at 250oC, H2/CO = 1.5 v/v and space velocity, SV=3 L/g-Fe/h. The CO conversion decreased to 30% when Fe loading was increased to 15 wt%. The CO conversion trend correlated to the size of the iron nanoparticles. For 6 wt% Fe/SiO2, the average size of iron nanoparticles was 8.6 nm whereas at 15 wt % iron loading, the average size of the iron nanoparticles was 13 nm. As the size of iron nanoparticles increased from 8.6 nm to 13 nm, the C5+ selectivity decreased from 20% to 11% whereas the selectivity for the light hydrocarbons increased from 55 % to 77%.